The present process and apparatus relate, in general, to the study of human responses to external stimuli such as light, vibration and sound and, more particularly, relate to the physiological responses of a human to sound stimuli and the use of such responses to test, select and/or design products which produce less stress or have a more pleasing sound output.
The study of the physiological response of a human to various sounds has increased in recent years. The effects of music, for example, on humans of various ages has been studied using sophisticated electrophysiological monitoring apparatus, such as electroencephalographs, electrocardiographs, electromyographs and even MRI scanners. Attempts have been made, for example, to determine whether or not music has a positive effect on the functioning of the brain while performing tasks such as mathematical problems.
In the industrial arena noise, vibration and harshness (NVH) effects have been studied in the automotive field. The general approach to such studies has been to try to isolate, eliminate or reduce the NVH level in automobiles so that the user does not have to endure long periods of time during which he or she is exposed to NVH levels that cause fatigue, irritability and/or drowsiness.
Studies directed to the effects of sound on humans also have included subjective approaches. Thus, panels or juries are asked to subjectively rank sound quality as between categories, such as, rough, sharp, metallic, whiney and hollow. Using such subjective rankings by panels of listeners the goal has been to try to predict sound-quality preferences, that is, to try to quantify in some manner the subjective impressions of the panel.
In some cases it is possible to simply isolate the user from the sound output, but in many cases such isolation is not practical or even possible. Moreover, in some instances, the sound output of a product can actually be pleasing, or made to be more pleasing. Thus, it has been a common experience in connection with mufflers for internal combustion engines that some mufflers will attenuate sound in a manner which is effective as to the decibel level, but nevertheless is irritating, stressful or unpleasant. Other mufflers, by contrast, are known to be subjectively more pleasing to the driver. Exactly why one muffler is annoying, while the other is pleasing, is only known in a general subjective sense, namely, that one has a harmony of sound or a consonance which is more appealing to the driver and to persons past whom the vehicle is driven.
Accordingly, it is an object of the present invention to provide a process and apparatus for selecting or designing products, such as exhaust mufflers for internal combustion engines, which produce an objectively demonstratable lessened mobilization of the body""s stress response mechanisms, or a more pleasing physiological response in humans.
A further object of the present invention is to provide a process and apparatus for producing or choosing a product having a multi-frequency sound output in which electrophysiological monitoring techniques are employed to objectively enhance product design or selection.
The process of the present invention has other objects and features which are set forth in, or will be apparent from, the following Best Mode of Carrying Out the Invention and the accompanying drawing.
The process and apparatus of the present invention is used to test and select or design a product having a sound output which produces less stress and therefore is more pleasing to a human listener. Briefly, the process comprises the steps of: sensing at least one physiological response of a subject while the subject listens to an initial sound output; changing at least one of the frequencies present in the initial sound output to produce a new sound output; repeating the sensing step for the new sound output; comparing the physiological response for the initial sound output with the physiological response for the new sound output; and selecting the sound output for use in choosing as between products or for use in designing a product, which selected sound output produces one of: a lower physiological stress response or a higher physiological pleasure response in the subject. The sensing step preferably is accomplished by sensing a physiological stress response of the subject using apparatus, such as a surface electromyography monitoring apparatus, a pulse sensor, a respiratory rate sensor, and/or combinations of such physiological response sensors. In apparatus which have complex, multi-frequency sound outputs, such as exhaust system mufflers, the changing and sensing steps are repeated many times to produce a plurality of new sound outputs, which outputs each are compared prior to performing the step of selecting the least stressful or most pleasing sound output.
The apparatus of the present invention comprises, briefly, an audio playback device, audio recordings of at least two sounds from products of different designs to be tested, and a physiological monitoring apparatus formed to be attached to a subject for monitoring the physiological response of the subject when listening to playback of the various audio recordings.